This invention relates to a device for folding sheet material for feeding to a user machine.
In particular, the present invention relates to a device for folding preshaped or punched pieces of cardboard or the like for feeding to a machine for packaging cigarettes into hinged lid packets, and is particularly adapted to constituting a folding station for a conveyor feeding said preshaped or punched pieces to said machine.
For feeding preshaped packaging pieces to said packaging machines and in particular to intermittent packaging machines, stepwise conveyors are notably used along which said preshaped pieces are subjected to at least one folding operation on a predetermined folding line.
The main object of this operation is not generally to give said preshaped pieces a three-dimensional shape, but to fold and glue below the preshaped pieces at least one peripheral portion thereof in order to strengthen certain parts.
In particular, in hinged lid cigarette packets, the part generally strengthened by folding back and glueing a peripheral portion or flap is the front wall of the lid, which is substantially the only part of the packet subjected to stress during the opening and closing thereof.
In the aforesaid conveyors, said flap is folded over a predetermined part of the feed path for the preshaped pieces by making these cooperate with a fixed folding element of helex shape which progressively folds said flap under the relative preshaped piece, about a predetermined folding line.
Folding a peripheral flap of a preshaped piece by a helical folding element gives rise to numerous difficulties which result in poor fold accuracy and the formation of wrinkles on the folded preshaped piece, arising mainly from the fact that the fold is necessarily made on a preshaped piece under movement and is not made at the various points along the folding line simultaneously, but rather in succession. These disadvantages may be ignored when the feed frequency of the preshaped pieces is below a relatively low value, but become unacceptable at very high frequencies, for example of the order of seven steps per second or more, corresponding to the frequency required for feeding a modern intermittent packaging machine.